Integrity testable multilayered filter device

ABSTRACT

The present invention relates to a device having two or more separate filtration layers that can be independently tested for integrity yet which allow for serial filtration through the two or more layers to obtain the desired characteristics such as retention. The device is made of two or more filtration areas, each containing one filter layer. Each area has one filtration layer and a first endcap bonded to a first end of the filter and a second endcap bonded to a second end of the filter. The areas are arranged concentrically around each other such that the first area is inward of the second area which is inward of a third area and the like. Each area is formed separately and integrity tested separately before final assembly. The first area is slid into the inside of the second area and then the two endcaps are either bonded to each, bonded to a third overall endcap or overmolded by a third endcap.

CROSS REFERENCE TO RELATED APPLICATIONS

The present utility patent application claims the benefit of U.S.Provisional Patent Application No.: 60/725,442, filed on Oct. 11, 2005.The entire contents of which are incorporated herewith in entirety.

The present invention relates to a device containing multiple layers offilters or membrane that is capable of being integrity tested. Moreparticularly, it relates to a device containing multiple layers offilters or membrane each of which is capable of being integrity testedindividually.

BACKGROUND OF THE INVENTION

Some filter devices contain two or more layers of filter or membranesandwiched together in order to gain certain performance characteristicssuch as retention. It is important that each layer remain integral anddefect free throughout the assembly process and during its use.

Normally integrity testing is done to the finished product containingthe multiple layers through an air diffusion test. This test wets outthe filter layers with a suitable liquid, such as water, alcohol ormixtures of the two (depending on whether the filter is hydrophilic orhydrophobic, the fluid used to test for integrity and the like). A gas,gases or liquid at a set pressure(s) is applied to one side of thewelted membrane and its flow on the other side is measured. If the flowincrease downstream is too quick or at a low pressure, this indicatesthat there is a defect in the filter or its sealing into the device. Theproblem with using this test in devices with multiple layers of membraneis that only the overall device is tested and the test can only indicateif there is a defect in all the layers. A defect in one layer may notprovide one with a conclusive indication of a defect especially if thelast layer is integral.

What is needed is a device that allows one to independently test eachlayer of membrane of an integrated multilayered device. The presentinvention allows one the ability to do so.

SUMMARY OF THE INVENTION

The present invention relates to a device having two or more separatefiltration layers that can be independently tested for integrity yetwhich allow for serial filtration through the two or more layers toobtain the desired characteristics such as retention. The device makessubassemblies of each layer and tests each layer for integrity before itis formed into the final device format.

The device is made of two or more filtration areas, each containing onefilter layer. Each area has one filtration layer and a first endcapbonded to a first end of the filter and a second endcap bonded to asecond end of the filter. The areas are arranged concentrically aroundeach other such that the first area is inward of the second area whichis inward of a third area and the like. Each area is formed separatelyand integrity tested separately before final assembly. The first area isslid into the inside of the second area and then the two endcaps areeither bonded to each, bonded to a third overall endcap or overmolded bya third endcap.

A process for making the device is also disclosed. Here a first filterpack is formed of a filter, preferably pleated to increase surface area,which is preferably cylindrical in form and having its two verticaledges (seam) joined together in a liquid tight arrangement. The firsthorizontal end of the filter is liquid tightly bonded to a first endcapand the second horizontal end of the filter is liquid tightly bonded toa second endcap. The first pack is then tested for integrity using anintegrity test such as an air-water diffusion test by wetting thefilter, applying a gas under pressure to one side of the filter, andmeasuring the flow of air on the other side of the filter. Othernon-destructive integrity tests can also be used. Upon successfulcompletion of the integrity test, a second pack is formed the same wayas the first pack. This pack has an inner dimension larger than theouter dimension of the first pack so as to form a concentric arrangementof the packs around each other. The second pack is then integrity testedand if it passes, the two packs are finally assembled so that the firstpack is inside the second pack which concentrically surrounds the firstpack. If desired additionally layers can be formed concentrically aroundthe first two.

These and other embodiments will become obvious to one of ordinary skillin the art from the specification and claims below.

IN THE DRAWINGS

FIG. 1 shows a first embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a multilayered filter device whereineach layer is formed separate from the other layers in a subassembly,each having a first and second endcap. A central porous core and anoutlet are also used. Each layer is then integrity tested and if theypass, they are assembled concentrically around each other and are sealedto each to form a liquid tight device. Preferably, an outer poroushousing is sealed outside the last filter layer and any fluid enteringthe housing must flow through each filter layer and then the core beforeexiting the outlet.

FIG. 1 shows a first embodiment of the present invention with twolayers. More than two layers can be made by the present invention aswell. The first filter layer 2 is sealed along its vertical edges (notshown) preferably by a seam (not shown) as is well-known in the art. Thetop horizontal surface 4 of the filter layer 2 is sealed to a first endcap 6 such as by polymer adhesion, solvent bonding or adhesives.Likewise the bottom horizontal surface 8 of the filter layer 2 is sealedto a second end cap 10 such as by polymer adhesion, solvent bonding oradhesives. A porous core 12 forms the inner surface of the first filterlayer in this embodiment although the core may be a separate piece ormay be part of another piece such as the outlet end cap (describedbelow) if desired.

As shown the first filter layer 2 is preferably cylindrical in shape,although other cross-sectional shapes such as oval, triangular orpolygonal can be used. Preferably the first filter layer 2 is pleated toincrease the available surface area.

Arranged concentrically outside around the first filter layer 2 is asecond filter layer 20. The second layer 20 is preferably cylindrical inshape although other cross-sectional shapes such as oval, triangular orpolygonal can be used and it preferably has the same shape as the firstfilter layer 2. Preferably the second filter layer 20 is pleated toincrease the available surface area. The second filter layer 20 issealed along its vertical edges (not shown) preferably by a seam (notshown) as is well-known in the art. The top horizontal surface 22 of thesecond filter layer 20 is sealed to a first end cap 24 such as bypolymer adhesion, solvent bonding or adhesives. Likewise the bottomhorizontal surface 26 of the second filter layer 20 is sealed to asecond end cap 28 such as by polymer adhesion, solvent bonding oradhesives. Preferably a porous spacer layer 30 is placed adjacent theinner surface of the second filter layer 20 and sealed to the top andbottom end caps 24 and 28.

As shown, the inner edges of the first and second end caps 6, 10 of thefirst filter layer 2 are liquid tightly sealed to the respective outersurfaces of the core 12. The inner edges of the first and second endcaps24, 28 of the second filter layer 20 are liquid tightly sealed to therespective outer surfaces of the first and second end caps 6, 10 of thefirst filter layer 2. Arranged concentrically outward and around thesecond filter layer 20 is a porous cartridge housing 32 that is liquidtightly sealed to the outer edges of the endcaps 24, 28 of the secondfilter layer 20. A top closed cartridge end cap 34 is sealed to thehousing 32, and top end caps 6, 24 of the first and second filter layers2, 20. A bottom cartridge end cap 36 having an outlet 38 is sealed tothe housing 32 and the bottom end caps 10 and 28 of the first and secondfilter layers 2, 20 to complete the cartridge.

In this manner, liquid which enters the housing 32 must flow through thesecond 20 and then the first filter layer 2 before entering the core 12and leaving the filter through the outlet 38.

As mentioned above, the present invention may have more than two layerswith each layer being assembled and arranged concentrically outward ofthe last. Once the outer most filter layer has been formed and sealedthe porous outer housing and top and bottom cartridge end caps areapplied.

A method of making the present device is to form the first layer as asubassembly comprised of at least the filter material and the top andbottom end caps. If desired, the core may be included as the inner wallof the subassembly or it may be a separate piece or incorporated as partof the bottom cartridge endcap. The second, and if desired, additionallayers, are then likewise formed as subassemblies of filter and at leasttop and bottom end caps. Preferably each additional subassembly has aporous spacer or support layer as its inner wall.

The inner diameter of an outer layer is substantially the same diameter(although it may be slightly smaller depending upon the sealing methodused (discussed below) as the outer diameter of the layer inward of itor of the core when referring to the first filter layer. At best thereshould be a slight interference fit between the adjacent layers as theyare assembled together. In this manner, there is a close fit between thesubassemblies so that they can be sealed together in a liquid tightmanner.

As each layer can be independently tested for integrity, one can use anyconventional test such as the air/water diffusion test in which themembrane is wet and a gas is applied to one side of the membrane at aset pressure or range of pressures. The flow of the gas is measured onthe other side of the membrane to determine whether the layer isintegral or if it has a defect such as a pin hole or a defective seal.

Alternatively, one can use a more sophisticated and sensitive test suchas a binary gas test as claimed in a co-pending application filed thisday entitled “Methods and Systems for Integrity testing of PorousMaterials” by John Lewnard. In this test, the selected filter layer iswetted with a liquid that is suitable for the binary gases used. Forexample one can use water, alcohol, mixes of water and alcohol and thelike depending upon the gases selected. Two gases are chosen such thatone has a high solubility in the liquid of choice and the other has alower solubility in that same liquid. Selected gases include but are notlimited to carbon dioxide, Freon, sulfur hexafluoride or other perfluorogases, noble gases and the like. The binary gas mixture is introduced asdescribed in FIGS. 2A-C in a predetermined amount relative to each otherand the amount of one or both of the gases is measured by the detectiondevice such as a gas chromatograph or a mass spectrometer on thedownstream side of the filter layer to determine whether there is ashift in the relative amount of each gas in the detected gas stream.Where the measured amount of gas differs from the predetermined amountof gas initially added to the system, a defect is detected. If nodifference in concentration is found, the layer is determined to beintegral. Integral, when referring herein to a porous material, meansnon-defective. The predetermined amount may be, for example, the amountof gas calculated to diffuse through the integral, wetted porousmaterial at a given temperature and pressure. The given temperature andpressure may be the temperature and pressure under which the test isconducted.

Another method of testing integrity is to use a liquid-liquid porometrytest as shown in U.S. Pat. Nos. 5,282,380 and 5,457,986 (DiLeo) whichmay also be used in the present invention.

The method used for testing integrity is not critical to the invention.Any method that provides one with a suitable value of integrity andwhich is not destructive to the device can be used.

Once all the layers have been made and successfully tested, they can beassembled. The easiest method is to simply slide the first layer intothe hollow center of the second layer, slide the combined first andsecond layer into the third layer, etc. Each pair of layers can besealed to each other before continuing to add any other layers if usedor they can all be sealed at once. A variety of methods are known forsealing plastics to each other and include but are not limited toadhesives, solvent bonding, heat or ultrasonic bonding and the like.

After all the layers have been assembled and sealed to each other, thetop and bottom endcaps are all sealed to a respective cartridge endcapand the outer housing to complete the assembly.

Alternatively, one can slide the subassemblies together, slide an outerhousing over the outermost layer and then place the entire assembly intoa mold and injection mold or overmold the cartridge endcaps over theendcaps of the layers and the housing to create a liquid tight sealingarrangement.

The device and methods of the present invention can be used with anyfilter media of any size that is capable of being integrity tested usinggases or liquids. They may be for example woven or non-woven filters orcast porous membranes. The filter media may be a microporous,ultrafiltration (UF), nanofiltration or reverse osmosis membrane formedof a polymer selected from olefins such as polyethylene includingultrahigh molecular weight polyethylene, polypropylene, EVA copolymersand alpha olefins, metallocene olefinic polymers, PFA, MFA, PTFE,polycarbonate, vinyl copolymers such as PVC, polyamides such as nylon,polyesters, cellulose, cellulose acetate, regenerated cellulose,cellulose composites, polysulphone, polyethersulphone, polyarylsulphone,polyphenylsulphone, polyacrylonitrile, polyvinylidene fluoride (PVDF),and blends thereof. The membrane selected depends upon the application,desired filtration characteristics, particle type and size to befiltered and the flow desired.

The other filter components such as end caps, inlets, outlets, housings,cores, ports, valves, etc., can be made of a variety of materials, suchas metal, ceramic, glass or plastic. Preferably, the components areformed of plastics, more preferably thermoplastics, such as polyolefins,especially polyethylene and polypropylene, homopolymers or copolymersthereof, ethylene vinyl acetate (EVA) copolymers; polycarbonates;styrenes; PTFE resin; thermoplastic perfluorinated polymers such PFA;nylons and other polyamides; PET and blends of any of the above.

1. A filtration device comprising: a. two or more concentric cylindrical layers of filters, b. a first layer of filter having a first and second two vertical edge joined together in a liquid tight arrangement, a first horizontal end of the first filter layer being liquid tightly bonded to a first endcap and a second horizontal end of the first filter layer being liquid tightly bonded to a second endcap; c. a second layer of filter having a first and second two vertical edge joined together in a liquid tight arrangement, a first horizontal end of the second filter layer being liquid tightly bonded to a first endcap and a second horizontal end of the second filter layer being liquid tightly bonded to a second endcap; d. a porous core and an outlet for the filter device; e. the first filter layer being arranged concentrically around the core and outlet of the device and having an inner diameter equal to or larger than an outer diameter of the core; f. the second layer having an inner diameter equal to or larger than an outer diameter of the first layer and being arranged concentrically around the first layer; g. the endcaps of the first layer being bonded in a liquid tight manner to the core, outlet and endcap of the second layer; and h. a porous outer cage arranged concentrically around an outer periphery of the second layer and being sealed to the outlet and the endcap of the second layer.
 2. A method of forming a filtration device having two or more layers of filter, each of which is capable of being tested for integrity independently, comprising the steps of: a. forming a first layer of filter having a first and second two vertical edge joined together in a liquid tight arrangement, a first horizontal end of the first filter layer being liquid tightly bonded to a first endcap and a second horizontal end of the first filter layer being liquid tightly bonded to a second endcap; b. testing the integrity of the first layer as formed in step (a); c. Forming a second layer of filter having a first and second two vertical edge joined together in a liquid tight arrangement, a first horizontal end of the second filter layer being liquid tightly bonded to a first endcap and a second horizontal end of the second filter layer being liquid tightly bonded to a second endcap; d. testing the integrity of the second layer formed in step (c); e. arranging the first layer concentrically around a porous core, the core containing an outlet; f. arranging the second layer concentrically around the first layer; g. bonding the core, first layer and second layer together in a liquid tight manner such that all liquid entering the second outer layer must flow through the first layer before reaching the core and then the outlet. 